Write, Read, Erase, Again And Again

Using a probe tip to shave away surface molecules, Temple University researchers expose 25-nm-wide patches (dark line at left), which serve as templates for reversible electrochemical formation of silver nanowires (right).

Credit: Courtesy of Eric Borguet

In The Groove

Using a probe tip to shave away surface molecules, Temple University researchers expose 25-nm-wide patches (dark line at left), which serve as templates for reversible electrochemical formation of silver nanowires (right).

Credit: Courtesy of Eric Borguet

In an advance reminiscent of the children's toy Etch A Sketch, researchers have developed a lithography method for preparing erasable nanometer-sized patterns. Similar to the plaything with which kids sketch with aluminum powder then wipe the slate clean and start over again, the new technique provides a way to prepare nanoscale metal patterns that can be erased and redrawn repeatedly.

Numerous procedures have been demonstrated in recent years for preparing nanoscale metal dots, wires, tubes, and other structures that may function as components of miniature electronic and optical devices. The processes are as varied as the structures themselves and rely on electrodeposition, electron-beam methods, scanning probe manipulations, and other distinct procedures.

Despite the unique qualities of the fabrication methods, they tend to share an undesirable distinction: By and large, they're irreversible-meaning that the nanostructures cannot be created, removed, and re-created efficiently in a "single pot."

Now, chemists at Temple University, in Philadelphia, have developed a straightforward method based on electrodeposition and atomic force microscopy that can be used to prepare closely spaced 25-nm-wide metal wires in an insulating medium. By controlling the electrochemical conditions, the researchers can form the patterns reversibly and repeatedly from a single aqueous reagent solution (Langmuir, published online Jan. 19, dx.doi.org/10.1021/la052489l).

Starting with a self-assembled monolayer of 1-hexadecanethiol on a gold surface submerged in a solution of silver ions, associate professor Eric Borguet and postdoc Kyoungja Seo use the microscope tip to shave away thiol molecules selectively, thereby exposing nanometer-sized bare patches of controllable size. Then by applying a suitable voltage to the gold surface (a few tenths of a volt), the team induces electrodeposition of silver in the bare patches.

After forming the wires (writing) and imaging the surface (reading), the group adjusts the voltage slightly, thereby causing the silver wires to dissolve back into solution (erasing). Then they image the surface again and repeat the entire process. According to the researchers, the thiol monolayer remains stable throughout multiple write-erase-rewrite cycles.

Borguet's group has taken an extremely well-established system, thiols on gold, and shown that it can be used in a fascinating, constructive, and almost simple manner, says Jillian M. Buriak, a chemistry professor at the University of Alberta, Edmonton, and a specialist in surface patterning. "I read this paper and thought, 'Why didn't I think of that?' " Buriak adds that the method broadens the capabilities of nanolithography and may be used to fabricate increasingly complex metal nanostructures.